1. Field of the Invention
The present invention relates sound generating devices and, more particularly, to a receiver with frequency response improvement.
2. Description of the Related Art
FIG. 1 shows a conventional mini receiver 60. The receiver 60 comprises a housing 62, which is comprised of a barrel-like yoke holder 64, a disk-like front cover plate 66 covering the front side of the yoke holder 64, and disk-like rear cover plate 68 covering the rear side of the yoke holder 64, a rear yoke 74 mounted inside the housing 62, the rear yoke 74 having an annular base 76 spaced from the rear cover plate 68 at a distance and a tubular body 78 forwardly extended from the inner diameter of the annular base 76, an annular magnet 82 disposed around the tubular body 78 of the rear yoke 74 without touching the periphery of the tubular body 78 and stopped at the front side of the annular base 76, a front yoke 84 disposed around the tubular body 78 of the rear yoke 74 and stopped at the front side of the annular magnet 82, a vibration diaphragm 86 stretched inside the housing 62 in front of the yokes 74 and 84, a voice coil 88 connected to the back side of the vibration diaphragm 86 at the center and suspended in the annular space between the front yoke 84 and the tubular body 78 of the rear yoke 74, and an acoustic paper 92 covering the rear open side of the tubular body 78 of the rear yoke 74. When applying an audio signal to the voice coil 88, the front yoke 84, the magnet 82 and the rear yoke 74 form a magnetic loop, thereby causing the voice coil 88 to vibrate the vibration diaphragm 86 corresponding to inputted video signal subject to Fleming's left hand rule, and to further produce sound.
It is well known that frequency response is an important index to judge the performance of a receiver. A long extension of the flat segment of frequency response curve means that the receiver can receive input signal of a relatively higher frequency or relatively lower frequency and maintain a constant output power. According to the design of the aforesaid conventional receiver, a better performance of frequency response to low frequency is achieved when increasing the internal space, i.e. the flat segment of frequency response curve extends in direction toward relatively lower frequency. On the contrary, when reducing the internal space of the receiver, the low frequency performance becomes poor. Because the aforesaid conventional receiver is commonly used in mobile apparatus, for example, a cellular telephone, there is a space limitation, i.e., low frequency performance is poor. Further, the performance of frequency response of the aforesaid conventional receiver to high frequency is still not good enough due to the effect of materials used and the limitation of internal space. The curve of imaginary line shown in FIG. 3 is a frequency response curve obtained from the aforesaid conventional receiver 60. As illustrated, the flat segment extends within the area between 300 Hz and 4 KHz, i.e., the output power of the receiver 60 drop drastically upon an input signal of frequency below 300 Hz or over 4 KHz.
Therefore, it is desirable to provide a receiver that eliminates the aforesaid drawbacks.